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Terminus Peptides

Laboratory standards

Identity testing

Establishing that a material is the substance it is labelled as — a separate question from how pure it is.

Identity testing answers one question: is this material the substance named on the label? It is logically prior to every other test, because a purity figure, a content determination and a stability profile all describe whatever is actually in the container, correct label or not.

How identity is established

  • Mass spectrometry, comparing the measured molecular mass against the mass calculated from the intended sequence. This is the usual first-line method for peptides.
  • Sequencing, either by tandem mass spectrometry fragmentation or by Edman degradation, which reads residues directly rather than inferring them from total mass.
  • Amino acid analysis, which hydrolyses the chain and quantifies the constituent amino acids, confirming composition without confirming order.
  • Comparison against a characterised reference standard under identical analytical conditions, where such a standard exists.

A robust identity conclusion generally rests on more than one method, because each technique has a class of errors it cannot detect. Two independent methods agreeing is a materially stronger position than one method returning a confident-looking number.

References